1. Field of the Invention
The present invention relates generally to thin films and methods for their deposition, and more particularly, provides diamond-like films, plasma beam deposition systems, and methods useful for production of diamond-like protective overcoats on magnetic recording media and other industrial applications.
In recent years, there has been considerable interest in the deposition of a group of materials referred to as diamond-like carbon. Diamond-like carbon can generally be defined as a metastable, high density form of amorphous carbon. Diamond-like carbon is valued for its high mechanical hardness, low friction, optical transparency, and chemical inertness.
Deposition of diamond-like carbon films often involves chemical vapor deposition techniques, the deposition processes often being plasma enhanced. Known diamond-like films often include carbon with hydrogen, fluorine, or some other agent. The durability and advantageous electrical properties of diamond-like carbon films have led to numerous proposals to apply these films to semiconductors, optics, and a wide variety of other industrial uses. Unfortunately, the cost and complexity of providing these advantageous diamond-like carbon films using known chemical vapor deposition processes has somewhat limited their use. Furthermore, while a wide variety of diamond-like carbon coating films have been deposited in laboratories, many of these films have been found to have less than ideal material characteristics.
A very different form of amorphous carbon is generally applied as a protective overcoat for magnetic recording media. Magnetic recording disks generally comprise a substrate having a magnetic layer and a number of underlayers and overlayers deposited thereon. The nature and composition of each layer is selected to provide the desired magnetic recording characteristics, as is generally recognized in the industry.
The information stored in magnetic recording media generally comprises variations in the magnetic field of a thin film of ferromagnetic material, such as a magnetic oxide or magnetic alloy. Usually, a protective layer is formed over the top of the magnetic layer, and a layer of lubricating material is deposited over the protective layer. These protective and lubricating layers combine to increase the reliability and durability of the magnetic recording media by limiting friction and erosion of the magnetic recording layer. Sputtered amorphous carbon films have gained widespread usage as protective overcoats for rigid magnetic recording disks.
Sputtered amorphous carbon overcoats have been shown to provide a high degree of wear protection with a relatively thin protective layer. Magnetic recording disk structures including sputtered amorphous carbon have been very successful and allow for quite high recording densities. As with all successes, however, it is presently desired to provide magnetic recording disks having even higher recording densities.
Recording densities can generally be improved by reducing the spacing between the recording transducer, called the read/write head, and the magnetic layer of the magnetic recording disk (or more specifically, between the read/write head and the middle of the magnetic layer). In modern magnetic recording systems, the read/write head often glides over the recording surface on an air bearing, a layer of air which moves with the rotating disk. To minimize frictional contact between the rotating disk and the read/write head, the disks surface is generally rougher (and the glide height therefore higher) than would otherwise be ideal for high density magnetic recording. Even if this glide height is reduced (or eliminated), the read/write head will be separated from the recording layer by the protective amorphous carbon overcoat. This protective layer alone may, to provide the desired media life, limit the areal density of the media. Generally, overcoat layer thicknesses are dictated by durability and continuity limitations. Sputtered carbon frequently becomes discontinuous at thicknesses below about 50Å. Thus, the durability requirements of rigid magnetic recording media generally dictate that the distance between the read/write head and the magnetic recording layer be maintained, even though this limits the areal density of the magnetic recording media.
It has previously been proposed to utilize known chemical vapor deposition techniques to deposit a variety of diamond-like carbon materials for use as protective coatings for flexible magnetic recording tapes and magnetic recording heads. Unfortunately, known methods for chemical vapor deposition of diamond-like materials, including plasma enhanced methods, generally subject the substrate to temperatures of over 500° C., which is deleterious for most magnetic disk substrates. Therefore, these known diamond-like carbon films do provide relatively good hardness and frictional properties, they have found little practical application within the field of rigid magnetic recording media, in which sputtered amorphous carbon protective overcoats are overwhelmingly dominant.
For these reasons, it would be beneficial to provide improved magnetic protective overcoats with improved read/write head frictional and glide characteristics (generally called stiction) for recording media. Preferably, such an improved overcoat will provide durability and reliability without having to resort to the density-limiting glide heights and/or protective overcoat thickness of known rigid magnetic recording media, and without subjecting the media substrates to excessive temperatures.
It would also be desirable to provide improved diamond-like carbon materials and methods for their deposition. It would be particularly desirable if such materials and methods could be utilized for practical rigid magnetic recording media with reduced spacing between the read/write head and the magnetic recording layer, ideally by providing a flatter, smoother, and thinner protective coating which maintained or even enhanced the durability of the total recording media structure. It would also be advantageous to provide alternative methods and systems for depositing such protective layers, for use in the production of magnetic recording media, as well as integrated circuits, optics, machine tools, and a wide variety of additional industrial applications.
2. Description of the Background Art
U.S. Pat. No. 5,182,132 describes magnetic recording media having a diamond-like carbon film deposited with alternating circuit plasma enhanced chemical vapor deposition methods. U.S. Pat. No. 5,462,784 describes a fluorinated diamond-like carbon protective coating for magnetic recording media devices. European Patent Application 700,033 describes a side-mounted thin film magnetic head having a protective layer of diamond-like carbon. European Patent Application No. 595,564 describes a magnetic recording media having a diamond-like protective film which consists of carbon and hydrogen.
U.S. Pat. No. 5,156,703 describes a method for the surface treatment of semiconductors by particle bombardment, the method making use of a capacitively coupled extraction grid to produce an electrically neutral stream of plasma. V. S. Veerasamy et al. described the properties of tetrahedral amorphous carbon deposited with a filtered cathodic vacuum arc in Solid-State Electronics, vol. 37, pp. 319-326 (1994). The recent progress in filtered vacuum arc deposition was reviewed by R. L. Boxman in a paper presented at the International Conference of Metallurgical Coatings and Thin Films located at San Diego in April of 1996. Electron cyclotron wave resonances in low pressure plasmas with a superimposed static magnetic field were described by Professor Oechsner in Plasma Physics, vol. 15, pp. 835-844 (1974).